PROJECT SUMMARY/ABSTRACT This application responds to Notice of Special Interest: Availability of Administrative Supplements for NIMH Grants to Expand Suicide Research. The supplemental funds will allow a new team to collect real-time ecological momentary assessment (EMA) data on suicidal and nonsuicidal self-injurious thoughts and behav- iors (SITB) in adolescent girls at risk for emerging suicidality. We focus on suicidal ideation and nonsuicidal self-injury as two of the earliest and strongest markers of future suicidal behavior. The parent grant utilizes functional neuroimaging and EMA to assess how sensitivity to social threats and rewards (such as rejection and acceptance from peers) from early- to mid-adolescence are associated with risk for depression and social anxiety disorder. Importantly, neurobehavioral responses to social threats and rewards also have potential rel- evance to understanding the development of SITB. The parent grant uses novel fMRI tasks to assess neural response to acceptance and rejection from virtual peers and a new EMA protocol that assesses daily percep- tions of socially threatening and rewarding interactions with peers. The study provides an ideal platform to ad- vance understanding of the development of SITB. First, interpersonal models of suicide propose that a threat- ened sense of social belonging is a key mechanistic factor in the suicide process. Our rich multilevel focus on how adolescents process positive and negative social interactions with peers could be leveraged to better un- derstand how SITB develops during adolescence. Second, the girls in our study (now ages 13-16) are currently going through a period of high risk for the onset of SITB. Additionally, two-thirds of the girls in the sample were recruited to be at temperamental risk for anxiety and depression, based on high shyness or fearfulness, which also places them at risk for SITB. Finally, suicide researchers have highlighted the need for data on near-term precipitants of SITB. The EMA design of the parent study provides an opportunity to obtain real-time data on factors theorized to play a proximal role in precipitating SITB, such as negative social interactions with peers. We propose to incorporate measures of SITB into the parent study for approximately 50 girls who will complete two-year follow-up assessments in Year 5 of the parent study. Measures will include structured clinical inter- views and questionnaires assessing suicidality and nonsuicidal self-injury (NSSI), and real-time measures of SI and NSSI integrated into a 16-day smartphone EMA protocol. This supplement will allow us to establish the acceptability of our EMA-based SITB protocol, build expertise in suicide within our team, and collect critical pi- lot data to generate future hypotheses. Specifically, we will use EMA of peer social threat/reward to identify proximal predictors of real-time SITB for further investigation, collect preliminary data testing whether height- ened neural sensitivity to social threat is a risk factor for concurrent and future SITB in adolescent girls, and explore brain-behavior interactions in the prediction of SITB. Results will be used to generate acceptability and pilot data to support a future larger scale investigation.